The structural genes coding for dopa decarboxylase and alcohol dehydrogenase have been isolated from D. melanogaster and cloned by others. The objective of the research proposed here is to isolate these genes from three related drosophilids (i.e., D. simulans, D. hydei, and D. virilis) and compare their internal structure and external sequence environment. Measurements to clarify the evolutionary relationships of the four species are also proposed. Isolation of the genes will be accomplished by construction of genome clone libraries in phage lambda of D. simulans, D. hydei and D. virilis and screening with cloned D. melanogaster probes now available. The rationale of the approach taken is that DNA sequences with regulatory function will be evolutionarily conserved as will important features of internal gene structure. Thus a search for regulatory signals and an understanding of functional aspects of internal gene structure can be carried out by a detailed comparison of structural genes and their flanking sequences in related species. Particular emphasis is placed on the sequence of DNA adjacent to the genes and on the number, size and location of intervening sequences in the coding region. Identification of aspects of genome organization which are conserved during evolution and analysis of the kinds of divergence which can occur, should provide new insights into both the evolution and present mode of action of developmentally regulated structural genes.